Method of coating metal for foodstuff containers



P 1940- c. G. SUMNER ET AL 2,215,166

METHOD OF COATING METAL FOR FOODSTUFF CONTAINERS Filed Feb. 7, 1938 3 Sheets-Sheet l Sept. 17, 1940- c. G. SUMNER ET AL METHOD OF COATING METAL FOR FOODSIUFF CONTAINERS Filed Feb. 7, 1938 5 Sheets-Sheet 2 HM W find. KW,

4PM m n as Sept. 17, 1940. c. GQSUMNER ET AL 7 2,215,166

METHOD OF COATING METAL FOR FOODSTUFF CONTAINERS Fi led Feb. '7, 1938 3 Sheets-Sheet 3 Patented Sept. 17,1940

UNITED STATES METHOD or ooA'rING METAL FOR roons'rurr CONTAINERS Cyril Gordon Sumner, Robert Ian Johnson, and William Clayton, London, England, assignors to Crosse & Blackwell Limited, London, England,

a. British company Application February '1, 1938, Serial No. 189,106

In Great Britain February 15, 1937 3 Claims. (c1.204 -1) It has been proposed to coat metal containers internally after fabrication, by electrodeposition of lacquer from an emulsion of the oil-inwater type. This process is applicable both to solid drawn containers which are formed by drawing from a single piece of sheet metaL'and to containers (without lids) which are made from two or more parts seamed or soldered together. When containers of the latter type are to be used 19 for hermetically sealing the contents, for example a foodstuff, it is necessary to solder the longitudinal joint in the body, whether or not this is lock-seamed, but one or both of the ends of the sealed container may be aflixed by double-seaming without soldering.

The. usual method of making an internally lacquered container, by fabrication from previously lacquered sheet, has the disadvantage that the forming operations are liable to damage the lacquer coating. This is principally true of the body of the container, since in addition to scratches caused by the body maker, the soldering of the longitudinal joint may scorch the lacquer. Furthermore, if the joint is of the lock-seamed 1 type, the coating is subjected to serve bending at the seam, with consequent tendency to rupture. This severe bending is obviated if the joint is formed by simple overlap, but in this case, metal may be exposed to contact with the food or other material, along the inside edge of the seam. In

the case of a lock-seam joint, metal may be exposed at the notches. On the other hand, the forming operations for the ends of the container may be made much less damaging to the lacquer 5 coating, and no bare edges need be exposed.

Furthermore the preferredform of the seam between the end and body of a. container varies according to the particular views of the can maker and in certain cases the seaming technique employed may result in the presence of a narrow but deep annular gap between the end and body of the container. This gap may occasionally give rise to some difiiculty in securing perfect lacquering by electrodeposition at this point as pinholes 45 are liable to appear deep down within the gap.

These difficulties may be largely overcome if the interior surface of the body of the container is lacquered by electrodeposition, after fabrication but before attachment of the bottom end.

50 By this means the longitudinal seam and any damage done to the tin coating during fabrication are completely covered with lacquer, and scratching or rupture of the lacquer is avoided. -While not so independent of the fabrication processes P as the method of lacquering, the complete container (apart from the lid), this method has the further advantage that the apparatus and operations for electrodeposition may be simplified or facilitated, owing to the fact that the partially completed container has no blank end, but is es- 5 sentially a tube. According to the present invention both ends of the container which may be lacquered by electrodeposition or formed from plate previously lacquered in the usual manner, are attached to the body after thelatter has been '10 lacquered by electrodeposition.

In an example of an apparatus adapted to lacquer a sequence of container bodies by electrodepositionjeach body is conveyed to an electrode station. The body is brought to rest, relative to the electrode, on a base preferably consisting of, or faced with, insulating material, and provided with a gasket of rubber or other elastic composition. When the electrode is in position inside the body, the latter is pressed ontothe base in such 2 a way that liquid may be introduced without leakage. A suitable emulsion is caused to fill the whole of the volume between the electrode and the inner surface of the container body, by introduction through an orifice in the base or by other means. The electrodeposition process is then carried out. The surplus emulsion is then withdrawn, and the container body is discharged from the electrode station. The body then passes on to be sprayed with wash liquor for removal of the emulsion adhering to the deposited lacquer film, and to be subjected to air jets or other means of removing adherent drops of wash liquor, before drying, and, if required, stoving the lacquer. Alternatively the spraying and blowing operations may be carried out before the body leaves the electrode station.

The electrode station or stations may be fixed and the container bodies may be conveyed through the machine in intermittent movement, 40 or the electrode stations may move in a definite closed path and the bodies may pass through the machine either in continuous or in intermittent movement. Coating of the container body by electrodeposition before, instead of after, affixing the bottom end, has the following advantages:

1. The tubular body may be filled, when in position, through the fixed base plate instead 01' through the electrode assembly.

2. The tube may be emptied while still in posi- 5 tion and means of overturning a can for emptying are not necessary.

3. Washing off the adherent emulsion is simplified since the flow of liquid may be unidirectional. When spraying a can with a blank end, the wash- 5 manipulation of handle ll.

ings must run out at the same end as wash liquor enters, and it is more diflicult to cover the whole surface effectively. In the case of a tube, a maximum efiiciency may be obtained by using a spraying nozzle, which moves downwards through the tube, sweeping the emulsion in front of it. The nozzle may rotate.

4. Similar considerations apply to the removal of adherent drops of wash liquor by air jets. These also may be swept down through the tube, whereas with a blank-ended can it is dificult to arrange jets to play in the right direction for re: movingthe drops out of the can.

The invention also includes the method of simultaneously lacquering or coating both the inside and outside of a tubular open ended can body, by electrodeposition; in this case the can body is readily treated while totally immersed in aqueous lacquer dispersion and the necessary mechanism is again much simpler than would be required for treatment of a blank-ended can.

The process may be applied to container bodies comprising one or more parts, provided that both ends are open. It may be applied to any metal or combination of metals suitable for use as containers, for example, in the case of foodstuff con-' tainers steel plate tinned on one 'or both sides, untinned steel, or aluminium may be used.

A further application is the internal coating of container bodies made from seamless or welded tube, where roller application of thevlacquer is impracticable.

The invention is also applicable to the treatment of container bodies made from prelacquered plate, for the purpose of covering the exposed portions by, for example, an air-drying lacquer.

Although lacquer is mentioned particularly, other materials suitable for food containers fall within the scope of this invention, for example, waxy materials may be electrodeposited from dispersions in aqueous media.

An example of the application of the invention is. more particularly described below with reference to the accompanying drawings, of which Figure 1 is a part sectional elevation of an electrode station in a machine adapted to coat single container bodies, Figure 2 is a plan of a section through the plane AB (Figs. 1 and 3) intersecting the container body, Figure 3 is an elevation in the plane XY (Fig. 2) and Figure 4 is a half-plan.

Referring to Figure 1, the container body I is held between a lower gasket 2 and an upper gasket 3, which may be of rubber or similar insulating material. A suitable emulsion or-other treat ing liquid is contained in a sump 4, from which it is displaced by downward movement of the electrode 5, so as to fill completely the volume between the body I and the electrode. Electrode 5 is carried by, but electrically insulated from, tube 6, which is slidably mounted in guide I. A chain 8 is attached to stud 9, and passes over a sprocket III to a counter-balance weight (not shown). Chain 8, stud 9, and sprocket Ill are duplicated on the other side of the machine. The up and down movement of the electrode is effected by Electrical contact with the electrode is made by an insulated wire passing down tube 8, the end being secured by clamp l2.

The upper gasket 3 is carried by a mounting it which is clamped to the fixed pillar it. The sump t carrying the lower gasket 2 is mounted on rod i5, which is capable of vertical movement in collar 56, the latter also being carried from. the fixed pillar i l. Vertical movement of rod i5 is obtained by actuation of the handle ll, working about a pivot it and coupled to rod i 5 through linkit).

Attached to sump are vertical pillars 2t, 25, to which are clamped blocks 22, 23 (Figs. 2 and 3, not shown in Fig. l) of insulating material, through eccentric mountings 2d, 25, the latter allowing of adjustment. Blocks 22, 23 carry spring-loaded metal arms 26 and 27, which engage with the outside of the container body and serve to make electrical contact therewith.

In operation of the machine, the electrode 5 is first raised by means of handle ii until clear of the upper gasket 3, and the sump t is lowered by means of handlel'i. A can body is placed in position on the lower gasket 2, and is held against arms 28, 2?, while handle W is raised to press the body into contact with the upper gasket 3. Electrode 5 is now lowered through the body by means of handle H, thus displacing liquor from the sump 4, into the volume between the electrode and the body, sufficient to bring the level above the top edge of the latter.

An electric current is then passed through the liquid between the electrode 5 and the body i which serves as the complementary electrode, in such a way as to effect the desired treatment. Electrode 5 is raised again to its upper position, sump 8 is lowered, and the treated body is withdrawn, after which it may be washed and dried by suitable means.

We declare that what we claim is:

1. In a method of fabricating open-ended tubular stock suitable for foodstuff containers, the.

steps of temporarily closing an end of the tubular quer into said tubular stock, electrodepositing a lacquer coating on said stock from said dispersion, and removing the surplus dispersion.

2. In a method of fabricating open-ended tubular stock suitable for foodstuff containers, the steps of temporarily closing an end of the tubular stock, supplying an aqueous dispersion of lacquer to cover the internal and external walls of said tubular stock, electrodepositing a lacquer on said stock from said dispersion, and withdrawing the surplus dispersion.

3. In a method of fabricating open-ended tubular stock suitable for foodstufl' containers, the steps of temporarily closing an end of the tubular stock, introducing an aqueous dispersion of lacquer into said tubular stock, electrodepositing a lacquer coating on 'said stock from said dispersion, removing the surplus dispersion, removing the temporary closure, and washing the coated stock by a washing liquid flowing through said stock.

CYRJL GORDON SUMNER. 65 

